docs: def _vertically_size_cells(rendered_rows):
          """Grow row heights to cater for vertically spanned cells that do not
          fit in the available space."""
          for r, rendered_row in enumerate(rendered_rows):
              for rendered_cell in rendered_row:
                  if rendered_cell.rowspan > 1:
                      row_height = sum(row.height for row in
                                       rendered_rows[r:r + rendered_cell.rowspan])
                      extra_height_needed = rendered_cell.height - row_height
                      if extra_height_needed > 0:
                          padding = extra_height_needed / rendered_cell.rowspan
                          for i in range(r, r + rendered_cell.rowspan):
                              rendered_rows[i].height += padding
          return rendered_rows